Decoupler with concentric clutching members

ABSTRACT

In an aspect, a decoupler includes a hub, a pulley, a torsion spring, a first spring driver fixed to the pulley, and having a first stop feature for the spring; a second spring driver mounted about the hub and not fixed to the pulley, and having a second stop feature for the spring, a driving clutch shaft mounted connected to the second spring driver, a driven clutch shaft mounted concentrically with the driving clutch shaft and drivingly connected to the hub, a one-way wrap spring clutch mounted about the hub and disposed to interconnect the driving and driven clutch shafts, and configured to transfer torque in a first direction between the driving and driven clutch shafts, and an axial biasing member acting between one of (i) the pulley and the driving clutch shaft and (ii) the hub and driven clutch shaft, to urge the driving and driven clutch shafts together.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication No. 61/728,495 filed Nov. 20, 2012 and from U.S. ProvisionalPatent Application No. 61/728,948 filed Nov. 21, 2012, the contents ofboth of which are incorporated herein in their entirety.

FIELD OF DISCLOSURE

This disclosure relates generally to the art of hub decouplers and moreparticularly to overrunning alternator decouplers.

BACKGROUND OF DISCLOSURE

FIG. 1 shows a prior art overrunning alternator decoupler 10. The maincomponents of the prior art decoupler 10 are:

-   -   a pulley 12;    -   a bearing 14;    -   a bearing cover 16;    -   a bushing 17;    -   a torsion spring 18;    -   a driving clutch member (in this case a drum) 20;    -   a one-way wrap spring clutch 24;    -   a driven clutch member (in this case a drum) 28; and    -   a hub 30.

In the prior art decoupler 10 the torsion spring 18 is connected inseries with the one-way wrap spring clutch 24. In operation, torque issupplied from the engine accessory drive belt (not shown) to rotate thepulley 12 in a first direction. The inner diameter of the pulley 26 hasa feature (not shown) that abuts an end of the torsion spring 18 totransfer force thereto. The other end of the torsion spring 18 isconnected to the driving clutch drum 20 (which is not fixed to thepulley 12 but mounted to rotate about an axis defined by the hub 30),thus transferring torque from the pulley 12 to the driving clutch drum20 via the torsion spring 18. The driven clutch drum 28 isconcentrically mounted with the driving clutch drum 20 and the one-waywrap spring clutch 24 is mounted within driving clutch drum 20 and thedriven clutch drum 28, i.e., the volutes or coils of the wrap springclutch 24 extend along the inners bores of the drive and driven drums20, 28. Thus when the torque is transferred in the first direction(which is capable of being reacted by the one-way wrap spring clutch),the wrap spring clutch coils transfer torque from the driving clutchdrum 20 to the driven clutch drum 28. The driven clutch drum 28 is fixedto the hub 30, thus transferring power to the alternator.

When the engine decelerates rapidly, for example during a wide-openthrottle shift, the inertia of the alternator causes the hub to overspeed the pulley causing the torque to reverse direction. In this casethe one-way wrap spring clutch does not couple the torque from the huband driven clutch drum to the driving clutch drum, whereby the hub anddriven clutch drum freewheel relative to the driving clutch drum,torsion spring, and pulley, and vice versa.

SUMMARY

There are at least two problems with the foregoing structure thatprevent transmission of very high loads typically seen in front endaccessory drive applications.

First, the wrap spring clutch is most highly stressed where it crossesfrom the driving member to the driven member. Any space between thesetwo members provides a place for the clutch to expand itself beyond theconfines of the clutching surfaces. The clutch can become over-stressed,and can break or jam between the members.

Second, the driving and driven members could lose their coaxialalignment. If the driving and driven members are not kept coaxial thewrap spring clutch could twist and becoming overstressed or lose grip onthe clutching surface of the driving and/or driven members. Any freerocking in the bearing, or wear in the bushing, can compromise thiscoaxial alignment.

In addition, when the hub overruns the pulley, the torsion spring couldbecome axially compressed to such an extent that it becomes coil bound(i.e., a state where the coils are mutually engaged with each other andbecome bound to one another) in which case the torsion spring would loseits isolating capability.

In an aspect, a decoupler is provided that ameliorates one or more ofthese problems.

In an aspect, a decoupler is provided, including: a hub; a pulleymounted about the hub; a helical coil torsion spring disposed about thehub; a first spring driver fixed to the pulley, the first spring driverhaving a first stop feature to transfer force to the spring; a secondspring driver mounted about the hub and not fixed to the pulley, thesecond spring driver having a second stop feature to receive force fromthe spring; a driving clutch drum mounted about the hub, the drivingclutch drum being connected to the second spring driver; a driven clutchdrum mounted concentrically about the hub with the driving clutch drum,the driven clutch drum being drivingly connected to the hub; a one-waywrap spring clutch mounted about the hub and disposed within the drivingclutch drum and driven clutch drum for transferring torque in a firsttorque flow path direction between the driving clutch drum and drivenclutch drum; and an axial biasing member acting between one of (i) thepulley and the driving clutch drum and (ii) the hub and driven clutchdrum, so as to force the driving and driven clutch drums together.

Preferably, one of the driving clutch member and the driven clutchmember fits within the other to provide an axially aligned fit.

Preferably, an anti-ramp ring is fixed to an inner bore of the pulleyand the second spring driver and the anti-ramp ring includecomplementary features for interlocking one another when an angulardisplacement between the second spring driver and anti-ramp reaches apre-selected limit at which point torque is transferred directly betweenthe anti-ramp ring and the second spring driver, bypassing torquetransfer via the torsion spring.

In another aspect, a decoupler is provided, comprising: a hub definingan axis and connectable to a rotating element; a pulley rotatable aboutthe axis in a first direction; a helical coil torsion isolation springdisposed about the hub, wherein the isolation spring includes aplurality of coils that are spaced axially from one another including afirst end coil at a first axial end of the isolation spring and a secondend coil at a second axial end of the isolation spring; a first springdriver fixed to the pulley, the first spring driver having a firstspring driver surface to transfer force to the spring and a first endcoil support surface for supporting at least a portion of the first endcoil; a second spring driver rotatable about the axis and not fixed tothe pulley, the second spring driver having a second spring driversurface to receive force from the spring, the second spring driverhaving a second end coil support surface for supporting at least aportion of the second end coil; a driving clutch member mounted aboutthe hub, the driving clutch member being connected to the second springdriver; a driven clutch member positioned axially adjacent the drivingclutch member and mounted concentrically about the hub with the drivingclutch member, the driven clutch member being drivingly connected to thehub; and a one-way wrap spring clutch mounted about the hub and disposedto interconnect the driving clutch member and the driven clutch member,the one-way wrap spring clutch being configured to transfer torque in afirst flow path direction between the driving clutch member and thedriven clutch member. The decoupler is characterized by a first overrunlimit surface, connected to the first spring driver, which engages asecond overrun limit surface, connected to the second spring driver,when an angular displacement of the second spring driver relative to thefirst spring driver in the first direction reaches a first selectedangular displacement, so as to prevent an increase in the angulardisplacement between the second and first spring drivers beyond theselected angular displacement, wherein at the first selected angulardisplacement any axial compression of the isolation spring resultingfrom rotation of the end coil support surface on the second springdriver relative to the first end coil support surface on the firstspring driver is sufficiently small to prevent the coils from binding toone another.

In another aspect, the first spring driver further includes a firsttorque limit surface that engages a second torque limit surface on thesecond spring driver when torque transferred from the first springdriver to the second spring driver through the spring causes angulardisplacement of the first spring driver relative to the second springdriver to reach a selected torque-induced angular displacement, whereinengagement between the first and second torque limit surfaces preventsan increase in the angular displacement of the first spring driverrelative to the second spring driver beyond the selected torque-inducedangular displacement, and during engagement of the first and secondtorque limit surfaces any increase in torque that is transferred fromthe first spring driver to the second spring driver is transferredthrough the first and second torque limit surfaces.

Optionally, the driving and driven clutch members are both drums and theone-way wrap spring clutch is disposed within the driving clutch drumand driven clutch drum for transferring torque in the first flow pathdirection between the driving clutch drum and driven clutch drum.

Optionally, the driving and driven clutch members are both shafts andthe one-way wrap spring clutch is disposed on the driving clutch shaftand the driven clutch shaft for transferring torque in the first flowpath direction between the driving clutch shaft and the driven clutchshaft.

Optionally, one of the driving clutch member and the driven clutchmember fits within the other to provide an axially aligned fit.

Optionally, an anti-ramp ring is fixed to an inner bore of the pulleyand the second spring driver and the anti-ramp ring includecomplementary features for interlocking one another when an angulardisplacement between the second spring driver and anti-ramp reaches apre-selected limit at which point torque is transferred directly betweenthe anti-ramp ring and the second spring driver, bypassing torquetransfer via the torsion spring.

In another aspect, a decoupler is provided, comprising: a hub definingan axis and connectable to a rotating element; a pulley rotatable aboutthe axis in a first direction; a helical coil torsion isolation springdisposed about the hub, wherein the isolation spring includes aplurality of coils that are spaced axially from one another including afirst end coil at a first axial end of the isolation spring and a secondend coil at a second axial end of the isolation spring; a first springdriver fixed to the pulley, the first spring driver having a firstspring driver surface to transfer force to the spring and a first endcoil support surface for supporting at least a portion of the first endcoil; a second spring driver rotatable about the axis and not fixed tothe pulley, the second spring driver having a second spring driversurface to receive force from the spring, the second spring driverhaving a second end coil support surface for supporting at least aportion of the second end coil; a driving clutch member mounted aboutthe hub, the driving clutch member being connected to the second springdriver; a driven clutch member positioned axially adjacent the drivingclutch member and mounted concentrically about the hub with the drivingclutch member, the driven clutch member being drivingly connected to thehub; and a one-way wrap spring clutch mounted about the hub and disposedto interconnect the driving clutch member and the driven clutch member,the one-way wrap spring clutch being configured to transfer torque in afirst flow path direction between the driving clutch member and thedriven clutch member. The decoupler is characterized by a first overrunlimit surface, connected to the first spring driver, which engages asecond overrun limit surface, connected to the second spring driver,when an angular displacement of the second spring driver relative to thefirst spring driver in the first direction reaches a first selectedangular displacement, so as to prevent an increase in the angulardisplacement between the second and first spring drivers beyond theselected angular displacement, wherein at the first selected angulardisplacement any axial compression of the isolation spring resultingfrom rotation of the end coil support surface on the second springdriver relative to the first end coil support surface on the firstspring driver is sufficiently small to prevent the coils from binding toone another.

In another aspect, the first spring driver further includes a firsttorque limit surface that engages a second torque limit surface on thesecond spring driver when torque transferred from the first springdriver to the second spring driver through the spring causes angulardisplacement of the first spring driver relative to the second springdriver to reach a selected torque-induced angular displacement, whereinengagement between the first and second torque limit surfaces preventsan increase in the angular displacement of the first spring driverrelative to the second spring driver beyond the selected torque-inducedangular displacement, and during engagement of the first and secondtorque limit surfaces any increase in torque that is transferred fromthe first spring driver to the second spring driver is transferredthrough the first and second torque limit surfaces.

Optionally, the driving and driven clutch members are both drums and theone-way wrap spring clutch is disposed within the driving clutch drumand driven clutch drum for transferring torque in the first flow pathdirection between the driving clutch drum and driven clutch drum.

Optionally, the driving and driven clutch members are both shafts andthe one-way wrap spring clutch is disposed on the driving clutch shaftand the driven clutch shaft for transferring torque in the first flowpath direction between the driving clutch shaft and the driven clutchshaft.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other aspects of the disclosure will be more readilyappreciated by reference to the accompanying drawings, wherein:

FIG. 1 shows a prior art decoupler; and

FIG. 2 is an elevation view of an engine including an embodiment of adecoupler;

FIG. 3 is an exploded perspective view of the decoupler shown in FIG. 2;

FIG. 4 is another exploded perspective view of the decoupler shown inFIG. 2;

FIG. 5 is a sectional side view of the decoupler shown in FIG. 2;

FIG. 6 is a magnified sectional view of a portion of the decoupler shownin FIG. 5; and

FIG. 7 is a sectional side view of another embodiment of a decoupler.

DETAILED DESCRIPTION Decoupler with Inboard Wrap Spring ClutchArrangement I.e. Drum-to-Drum

Reference is made to FIG. 2, which shows an embodiment of a decoupler100 positioned for use between a shaft 106 a from an accessory such asan alternator 106, and an accessory drive belt 104 that is driven by acrankshaft 62 on a vehicle engine 63 (through a pulley 67). The belt 104may be used to transfer torque from the crankshaft 62 to driveaccessories such as the alternator 16, via a pulley 112, a powersteering pump 68 via pulley 69, a water pump 70, via pulley 71, an airconditioning compressor 72 via pulley 73, and/or any other suitableaccessories. A belt tensioner is shown at 74 for maintaining belttension, and an idler is shown at 75 for maintaining a suitable amountof belt wrap on selected components. The terms ‘pulley’ and ‘belt’ areused for convenience, however it will be understood that the belt may beany suitable endless drive member and the pulleys may instead be anysuitable rotary drive member that can transfer power to and from theendless drive member.

Referring to FIG. 2, the decoupler 100 permits torque to be transferredfrom the pulley 112 to the shaft 106 a of the alternator 106 duringrotation of the pulley 112 in a first direction (indicated in FIG. 1 atD1), while permitting overrunning of the shaft 106 a in the firstdirection relative to the pulley 112 in situations when there is adeceleration of the pulley 112 relative to the shaft 106 a. Thedecoupler 100 includes a pulley 112 mounted for rotation about a hub 130(which may also be referred to as a shaft connection member 130), via aball bearing 114 mounted about a shouldered portion 130D of the hub 130.The hub 130 connects to the shaft 106 a of the alternator 106. Thepulley 112 has an outer drive surface 112A is connected to an endlessdrive member (such as a V-belt) shown at 104 of an engine front endaccessory drive system. The pulley 112 also has an inner bore 1128 thathouses the majority of the decoupler components.

A spring driver 132 is fixed to the inner bore 1128 of the pulley 112and mounted about the hub 130 via a bushing 117. A helical coil torsionspring 118 is connected to the spring driver 132. More particularly, thespring driver 132 has a stop feature 132A on an inner axial surfacethereof, including a first spring driver surface 132B, for abutmentagainst a first end 118A of the torsion spring 118. The spring driver132 also includes an end coil support surface 132C for supporting an endcoil of the torsion spring 118. The height of the support surface 132Cis sized to provide an incline or ramp so as to conform to theunstressed slope or helix angle of the torsion spring 118.(Alternatively, the spring driver 132 may be configured so that itsinner axial surface is inclined or ramped along 132D to abut a longerstretch or run of the end coil.)

A driving clutch drum 120 is mounted about the hub 130 and a springdriver 122 is fixed to the driving clutch drum 120. The spring driver122 includes a stop feature 122A, including a second spring driversurface 122B, for transfer of force with a second end 118B of thetorsion spring 118. The spring driver 122 also includes an end coilsupport surface 122C for supporting an end coil of the torsion spring118. The height of the end coil support surface 122B is sized to providean incline or ramp so as to conform to the unstressed slope or helixangle of the torsion spring 118. (Alternatively, the spring driver 122may be configured so that its inner axial surface is inclined or rampedalong 122D to abut a longer stretch or run of the end coil.)

A spring anti-ramp ring 140 is fixedly connected to the inner bore 112Bof the pulley, such as through a press fit.

A thrust washer 134 and a wave spring 136 are disposed in the anti-rampring 140 to provide an axial force against the driving clutch drum 120.More particularly, the anti-ramp ring 140 has a radial wall 140A thatseats the thrust washer 134. The driving clutch drum 120 has a foldedbutt end 120B that terminates in a planetary flange 120C against whichthe spring driver 122 bears. The wave spring 136 is disposed over thebutt end 120B and bears between the planetary flange 120C and the thrustwasher 134/anti-ramp ring 140.

The anti-ramp ring 140 also includes an axial wall 140B with axiallyextending arcuate tabs 140C that define arcuate slots 140D in the ring140. The planetary flange 120C of the driving clutch drum 120 alsoincludes radially extending tabs 120D that are disposed in the arcuateslots 140D and cooperate with the arcuate tabs 140D as discussed ingreater detail below.

A driven clutch drum 128 is mounted about the hub 130. As seen best inthe detail view of FIG. 6, the drive clutch drum 128 has an inner boreend portion 128A with a wider inner diameter than an immediatelyadjacent inner bore portion 128B. A flat radial end face 128C is definedat the junction between the bore portions 128A and 128B. The drivingclutch drum 120 fits within the inner bore end portion 128A of thedriven clutch drum 128 and seats against its flat radial end face 128C.

The driven clutch drum 128 also includes an integrated ring gear 128D.The hub 130 also features a splined ring 130C on the outer surfacethereof for driving interconnection with the drive clutch drum ring gear128D.

The hub 130 has a bore 130A at one end thereof for connection to analternator hub 106 a (FIG. 2). The other end of the hub 130 has areceptacle 1308 for receiving the head of a driving tool.

Axial Alignment

In operation, torque is supplied from the endless drive element torotate the pulley 112 in a first direction. The spring driver 132, beinglocked to the pulley 112, drives the torsion spring 118 via the stopfeature 132A and the first spring driver surface 132B that abuts thefirst end 118A of the torsion spring 118. When the torque flow path isin a first direction the torsion spring 118 expands radially. The otherend 1188 of the torsion spring 118 drives the second spring driversurface 122B of the stop feature 122A of the spring driver 122. This, inturn, rotates the driving clutch drum 120 in the first direction. Thedriving clutch drum 120 is pushed axially toward the driven clutch drum128 by the wave spring 136 which, as discussed above, is supported bythe anti-ramp ring 140 that is fixed to the pulley. (Consequently, whilethere may be some angular displacement of the driving clutch drum 120relative to the pulley 112 as the torsion spring 118 resilientlytransfers load between the pulley 112 and the driving clutch drum 120,the latter should not rotate at high speed relative to the former.)Thus, as seen best in the detail view of FIG. 6, the wave spring 136forces the clutching drums 120, 128 tightly together, eliminating anyspace for the coil(s) of the wrap spring clutch 124 to move into. Inaddition, one of the clutching drums (driving clutch drum 120) fitsinside the other (driven clutch drum 128), maintaining alignment. Whenthe torque flow path is in the first direction, due to the frictionagainst the inner bores of the driving and driven clutch drums 120, 128,the wrap spring clutch 124 is urged to expand against the inner bores ofthe driving and driven clutch drums 120, 128. The wrap spring clutch 12thus couples the driving and driven clutch drums 120, 128, and torque istransferred between the drums 120, 128. In turn, the driven clutch drum128 rotates the hub 130 via the splined interconnection therebetween andthe hub 130 rotates the alternator.

The embodiment shown and discussed above utilized a wave spring as anaxial biasing member. However, any other mechanism that accomplishes thesame function, such as a compression spring, could be utilized in thealternative. Moreover, the axial biasing member was shown acting betweenthe pulley and the driving clutch drum 120. However, the axial biasingmember could also be mounted to act between the hub 130 and the drivenclutch drum 128. Likewise, the driving clutch drum 120 is shown asfitting into the driven clutch drum 128 but the reverse is equallyviable. Similarly, a number of components that are shown as separateparts could be integrated with other parts. For example, the springdriver 132 and anti-ramp spring 140 could be integrally formed with thepulley 116. Likewise, the driven clutch drum 128 could be integrallyformed with the hub 130.

Anti-Ramp Feature

When the engine decelerates rapidly, for example, during a wide-openthrottle shift, the inertia of the alternator causes the hub 130 tooverrun the pulley 112, which causes the torque flow path to reversedirection. In this case the one-way wrap spring clutch 124 is urged toconstrict and thus does not couple or transfer torque between the drivenclutch drum 128 and the driving clutch drum 120. Consequently, thedriving clutch drum 120, torsion spring 118, and pulley 112 rotatefreely relative to the hub 130 and the driven clutch drum 128, and viceversa.

In this freewheeling state the hub 130 and the driven clutch drum 128rotate at the same speed. The pulley 112 decelerates due to the reducedtorque from the endless drive element. However, friction between thedriving clutch drum 120 and the wrap spring clutch 114 as well as theinertia of the driving clutch drum 120 could cause it to move at adifferent rate than the spring driver 132. This difference in speedcould cause the second spring driver surface 122B of the spring driverstop feature 122A to move away from the torsion spring end 118B. As theend coil of the torsion spring 118 lies effectively on an inclineprovided by the end coil support surface 120C, the torsion spring 118could rewind from its drive position (where torsion spring end 118Bcontacts the second spring driver surface 122B) so as to compressaxially. In this event the coils of the torsion spring 118 could becomemutually engaged and bind against one another, and thereafter notunwind, in which case the decoupler 100 would lose its isolatingfunction.

The problem is curtailed by causing the fixedly connected driving clutchdrum 120 to interlock against the anti-ramp ring 140 when the angulardisplacement between the two components reached a predetermined limit.This angular limit is defined by the length of the arcuate slots 140D ofthe anti-ramp ring 140. More particularly, the anti-ramp ring 140 hasfirst overrun limit surface 140E at the edge of the arcuate slot 140Dand the driving clutch drum 120 has an overrun limit surface 120E at theedge of the radially extending tab 120D. Because of the presence of thefirst and second overrun limit surfaces 140E and 120E, the drivingclutch drum 120 cannot overrun the spring driver 132 by more than aselected angular distance before the first and second overrun limitsurfaces 140E and 120E engage each other. The angular displacement limitis preferably selected to preclude axial binding of the torsion spring118 to the point where its coils can bind one other. For example, theangular displacement limit can be set so that the first and secondoverrun limit surfaces 140E and 120E contact one another at the onset offreewheeling. Alternatively, the angular displacement limit can be setto allow the torsion spring 118 to axially compress for a limited amountbut with a sufficient margin of safety to ensure that its coils do notbind. For example, the angular displacement limit can be set to precludethe spring coils from contacting one another. When the driving clutchdrum 120 and the pulley 112 interlock, torque or rotary power istransferred directly therebetween bypassing torque transfer through thetorsion spring 118.

In the embodiment shown, the first and second overrun limit surfaces140E, 120E are provided on the arcuate slot 140D and the radiallyextending tab 120D. However the overrun limit surface 140E may beincorporated into the anti-ramp ring 140 or the pulley 112 or the springdriver 132 in any other suitable way and the overrun limit surface 120Emay likewise be incorporated into the driving clutch drum 120 or thespring driver 122 in any other suitable way. In the embodiment shown,two overrun limit surfaces 140E and two overrun limit surfaces 120E areprovided. However, there could be one of each surface 140E and 120Eprovided or three or more of each surface 140E and 120E provided.

Torque Limiting Feature

As shown in FIGS. 2 and 3, the anti-ramp ring 140 may have a firsttorque limit surface 140F at an opposing edge of the arcuate slot 140Dand the driving clutch drum 120 may have a second torque limit surface120F at an opposing edge of the radially extending tab 120D. Duringoperation of the decoupler 100, when the pulley 112 is driving the hub130, the first and second torque limit surfaces 140F and 120F are spacedapart rotationally by a selected angular displacement. In general,torque applied to the pulley 112 by the endless drive element 104 (FIG.2) is transferred from the pulley 112 to the spring driver 132, then theisolating torsion spring 118, then the driving clutch drum 120, andfinally to the hub 130 via the driven clutch drum 128 and wrap springclutch 124. As the torque transferred increases, the amount of torsionalflexure or twist present in the torsion spring 118 increases and theangular displacement between the spring driver 132 and the drivingclutch drum 120 increases such that the first and second torque limitsurfaces 140F and 120F approach each other. If the torque reaches aselected threshold torque, the angular displacement between the springdriver 132/anti-ramp ring 140 and the driving clutch drum 120 changessuch that the first and second torque limit surfaces 140F and 120Fengage each other. Due to their engagement, any increase in torquetransferred beyond this selected threshold torque is transferred throughthe first and second torque limit surfaces 140F and 120F and not throughthe torsion spring 118. Thus the first and second torque limit surfaces140F and 120F serve to limit the maximum amount of torque that thespring 118 will transfer. This can be useful in preventing the spring118 from becoming overstressed, and/or in preventing the spring 118 frombecoming so uncoiled that it engages and galls the radially innersurface of the pulley 118.

In the embodiment shown, the first and second torque limit surfaces140F, 120F are provided on the arcuate slot 140D and the radiallyextending tab 120D. However the torque limit surface 140F may beincorporated into the anti-ramp ring 140 or the pulley 112 or the springdriver 132 in any other suitable way and the overrun limit surface 120Fmay likewise be incorporated into the driving clutch drum 120 or thespring driver 122 in any other suitable way. In the embodiment shown,two first torque limit surfaces 140F and two second torque limitsurfaces 120F are provided. However, there could be one of each surface140F and 120F provided or three or more of each surface 140F and 120Fprovided.

In the embodiment shown, the anti-ramp ring 140 and driving clutch drum120 include both the overrun limit surfaces 140E and 120E (i.e. theanti-ramp feature) and torque limit surfaces 140F and 120F (i.e. thetorque-limiting feature). However, it is alternatively possible for theanti-ramp ring 140 and driving clutch drum 120 to include one of thesefeatures and not the other.

Preloading the Torsion Spring

The overrun limit surfaces 140E and 120E have been described as beingused to prevent the incline provided by the end coil support surface120C on the driving clutch drum 120 from rotating during an overrunsituation and causing compression and binding of the torsion springcoils. However, in some embodiments, the overrun limit surfaces 140E and120E may be positioned so that, when the decoupler is in a rest state,there is a selected amount of preload in the torsion spring 118. In suchembodiments, when the decoupler is in a rest state, the first and secondoverrun limit surfaces 140E and 120E would abut each other, and thepositions of the spring driver surfaces 122B and 132B may be positionedrelative to the overrun limit surfaces 140E and 120E so as to causeflexure of the torsion spring 118. Due to the abutment of the overrunlimit surfaces 140E and 120E the spring 28 is thus preloaded. As aresult, any torque input from the pulley 112 would have to overcome thepreload in the torsion spring 118 in order to move the second springdriver 122 relative to the first spring driver 132. Thus for a selectedrange of torques the overrun limit surfaces 140E and 120E remain inabutment with one another. As a result of this abutment, at least someof the ‘chatter’ or ‘rattle’ that might be present in some non-preloadeddecouplers in certain situations may be reduced or eliminated. Such asituation may be, for example, when there is a relatively low load onthe alternator (to which the decoupler may be connected) and there arerelatively high torsionals from the engine. Torsionals are torsionalvibrations (variations in the speed of the crankshaft of any internalcombustion engine) that are the natural result of the movement of thereciprocating movement of the pistons of such engines. Torsionals can beparticularly strong in certain types of engines and at certain RPM, suchas, for example, at idle in engines with low cylinder counts (e.g. two-,three- or four-cylinder engines) and/or in some diesel engines. Thesetorsionals can be transmitted to the endless drive element from thecrankshaft and from the endless drive element into the decoupler. Byreducing or eliminating chatter that can result from such torsionals,the decoupler may operate more quietly, and may have an improved servicelife. In embodiments where the overrun limit surfaces 140E and 120E areprovided to preload the spring 118, the overrun limit surfaces 140E and120E may be referred to as spring preload surfaces 140E and 120E.

Decoupler with Outboard Wrap Spring Clutch Arrangement (i.e.Shaft-to-Shaft)

FIG. 7 shows a second preferred embodiment of a decoupler 200 thatutilizes a concentric drum arrangement interconnected by an outboard onewrap spring clutch as discussed below.

The decoupler 200 is similar to the decoupler 100. The components thatare the same are given the same reference numbers and are not discussedfurther. The components that are similar but situated in a differentlocation are given the same but primed reference numbers.

In the decoupler 200, the one-way wrap spring clutch 124′ is situatedoutboard of a driving clutch shaft 120′ (that is similar to drivingclutch drum 120 except that it is engaged on its outer surface 202instead of its inner surface with the one-way wrap spring clutch 124′)and driven clutch shaft 128′ (that is similar to driving clutch drum 128except that it is engaged on its outer surface 204 instead of its innersurface with the clutch 124′) and is configured to contract about theouter surfaces 202 and 204 of the driving clutch shaft 120′ and drivenclutch shaft 128′ to couple and transfer torque along a first torqueflow path from the driving clutch shaft 120′ to the driven clutch shaft128′. The one-way wrap spring clutch 124′ is not configured to transfertorque in a reverse torque flow path from the driven clutch shaft 128′to the driving clutch shaft 120′. The decoupler 200 may otherwiseoperate similarly to the decoupler 100.

As described above, the wrap spring clutch 124 engages driving anddriven clutch drums 120 and 128, and the wrap spring clutch 124′ engagesdriving and driven clutch shafts 120′ and 128′. More generally, the wrapspring clutch (124 or 124′, as appropriate) engages driving and drivenclutch members, which are concentric and axially adjacent one another.In some embodiments the driving and driven clutch members are drums. Inother embodiments the driving and driven clutch members are shafts.

Those skilled in the art will understand that a variety of othermodifications may be effected to the embodiments described hereinwithout departing from the scope of the appended claims.

The invention claimed is:
 1. A decoupler, comprising: a hub; a pulleymounted about the hub; a helical coil torsion spring disposed about thehub; a first spring driver fixed to the pulley, the first spring driverhaving a first stop feature to transfer force to the spring; a secondspring driver mounted about the hub and not fixed to the pulley, thesecond spring driver having a second stop feature to receive force fromthe spring; a driving clutch member mounted about the hub, the drivingclutch member being connected to the second spring driver; a drivenclutch member positioned axially adjacent the driving clutch member andmounted concentrically about the hub with the driving clutch member, thedriven clutch member being drivingly connected to the hub; a one-waywrap spring clutch mounted about the hub and disposed to interconnectthe driving clutch member and the driven clutch member, the one-way wrapspring clutch being configured to transfer torque in a first flow pathdirection between the driving clutch member and the driven clutchmember, and configured to inhibit torque flow in a second direction thatis opposite the first direction between the driven clutch member anddriving clutch member; and an axial biasing member acting between one of(i) the pulley and the driving clutch member and (ii) the hub and drivenclutch member, so as to urge the driving and driven clutch memberstogether.
 2. A decoupler as claimed in claim 1, wherein the drivingclutch member is a driving clutch drum and the driven clutch member is adriven clutch drum, wherein the one-way wrap spring clutch is disposedwithin the driving clutch drum and driven clutch drum for transferringtorque in the first flow path direction between the driving clutch drumand driven clutch drum.
 3. A decoupler as claimed in claim 1, whereinthe driving clutch member is a driving clutch shaft and the drivenclutch member is a driven clutch shaft, wherein the one-way wrap springclutch is disposed on the driving clutch shaft and driven clutch shaftfor transferring torque in the first flow path direction between thedriving clutch shaft and driven clutch shaft.
 4. A decoupler as claimedin claim 1, wherein one of the driving clutch member and the drivenclutch member fits within one another.
 5. A decoupler as claimed inclaim 1, including an anti-ramp ring fixed to an inner bore of thepulley and wherein the second spring driver and the anti-ramp ringinclude complementary features for interlocking one another when anangular displacement between the second spring driver and anti-rampreaches a pre-selected limit at which point torque is transferreddirectly between the anti-ramp ring and the second spring driver,bypassing torque transfer via the torsion spring.